Real-time bidding (“RTB”) is a way of selling online advertising inventory. RTB allows an individual ad impression to be put up for bid in real time. This is done through a programmatic on-the-spot auction, which is similar to how certain financial markets operate.
For example, an OpenRTB API Specification, available from the Interactive Advertising Bureau at www.iab.net/guidelines/rtbproject, specifies contents of a bid request message sent by an auction service such as ad exchange (representing a publisher) to several bidder services each representing one or more advertisers, inviting the bidder services to bid on the opportunity to present an ad in an available placement on a web page that a particular user has requested from the publisher. The bid request includes information about the publisher and the placement, and any information the auction service has about the identity of the user and the user's device. Any of the bidder services interested in buying the impression can reply with a bid response containing a bid amount; the highest-bidding bidder service has the opportunity to present an advertising message in the placement, and is charged for this opportunity.